The present invention relates to computer generated graphics, in particular, the modeling and rendering of realistic graphics, focusing on fine-scale geometric features and associated visual effects of such features.
Computer graphics are used in many different applications including computer games, movies and web pages. With the capability of more powerful computers, realistic graphics are becoming more desired in order to provide a more realistic experience to the computer user.
Accurate computer rendering of fine-scale geometric features and associated visual effects yields vivid object appearance. This level of detail, commonly referred to as mesostructure, lies between that of meshes, which provide an efficient representation of gross shape, and bi-directional reflectance functions (BRDFs) that describe the light scattering effects of micro-scale material structure. The high-frequency visible geometry of mesostructure leads to complex visual effects including fine-scale shadowing, occlusion and silhouettes. These characteristics each contribute to realistic appearance, but are also difficult to render efficiently.
Mesostructures are typically rendered using techniques such as bump mapping, horizon mapping or displacement mapping. In summary, bump mapping perturbs mesh normals to coincide with the geometric detail to provide basic shading but not shadowing, occlusion, and silhouettes. Horizon mapping improves realism by adding self-shadows, but occlusion and silhouettes are still missing. Displacement mapping lacks shadowing, but provides occlusion and silhouettes. In addition, although conventional displacement mapping can be implemented in hardware, its performance for mesostructure rendering is limited by the large number of vertices that result from the considerable mesh subdivision required.
An image-based approach to mesostructure rendering is to sample surface appearance under various lighting and viewing directions. This technique is commonly referred to as a bi-directional texture function (“BTF”). Although characteristics such as shading, self-shadowing and occlusion are realized, silhouette characteristics are lacking. Similarly, a polynomial texture map (“PTM”) can incorporate shading and self-shadowing attributes, but lacks occlusion and silhouettes.
Accordingly, there is a clear need for improvements in realistic, mesostructure computer-renderings. Although a new method and system to render mesostructures with shadowing, occlusion and silhouette attributes would by itself be beneficial, an algorithm realizing some or all of these features that can be quickly and/or efficiently employed would also be beneficial.